Engine coolants for automotive vehicles usually contain a solution of ethylene glycol and a small percentage of diethylene glycol diluted with water to make an approximately 50-50 mixture or lower depending on the desired freezing point for the solution. Most companies which manufacture or distribute ethylene glycol add a corrosion inhibitor to the solution to protect the metal components of the system; especially the radiator. These inhibitors are usually a mixture of one or more inorganic salts, such as phosphates, borates, nitrates, nitrites, silicates or arsenates, and an organic compound, such as benzotriazole, tolyltriazole or mercaptobenzothiazole. The solution is generally buffered to a pH of 8 to 10 to reduce iron corrosion and to neutralize any glycolic acid formed in the oxidation of ethylene glycol.
As the number of automobiles requiring coolant system servicing rises to 50% after two years of normal passenger car service, it is extremely important that the coolant mixture contain 50 to 55% of properly inhibited ethylene glycol to prevent corrosion of conventional copper-brass radiators. With the advent of aluminum radiators which are more susceptible to corrosion than copper-brass units, the use of a proper amount of corrosion inhibitor in the coolant solution becomes more critical. A reduction of the coolant mixture to 33% ethylene glycol and 67% water will increase metal corrosion significantly; especially in higher temperature coolant systems which are becoming more common with the increased use of emission controls.
To prevent corrosion, the inhibitor concentration must be maintained at a proper level to prevent corrosion problems occurring if the coolant is lost through leakage or boil-off or if the inhibitor efficiency decreases with age. To solve the problem, the inhibitor concentration must be correctly measured and additional inhibitor added when needed. The present invention provides a device to overcome the above problems.